This invention relates generally to ignition fuzes and more particularly to a non-detonative linear ignition fuze suitable for use in gas generators and other applications requiring substantially instantaneous ignition of a material distributed along the exterior length of the fuze.
Linear ignition fuzes of the prior art generally comprise a core of non-detonating, ignitive material comprising a mixture of particulate fuel, oxidant, and a binder encased within a frangible sheath, with a longitudinally extending gas channel adjacent to the ignitive material of the core. The gas channel is defined by the shape and location of the strands that define the elongated core in relationship to the inner surface of the sheath circumscribing the core. U.S. Pat. No. 4,220,087 to Posson (the ""087 patent) discloses a linear ignition fuze in which the core is encased in a tubular sheath having a circular or an elliptical cross section of uniform wall thickness. The core comprises a bundle of three or more cylindrical strands or other shapes that form gas channels against the curved walls of the sheath and or between the cylindrical bundles forming the core. The linear ignition fuze disclosed in the ""087 patent has a number of drawbacks, including the high cost associated with manufacturing the multiple strand core or the irregularly shaped core necessary to form the gas channels against the circular or elliptical side walls of the sheath.
The present invention comprises an improved linear ignition fuze in which the inner surface of the sheath has an irregular cross section such that the sheath is capable of forming a gas channel against a single strand core having a substantially circular (e.g. circular or elliptical) cross section. According to one embodiment of the invention, the sheath wall is of a non-uniform thickness having a cylindrical outer surface and a polygonal inner surface. The gap formed between the apexes of the polygonal inner surface and the substantially cylindrical core form the gas channels, while the contact between the side walls of the polygonal inner surface and the cylindrical core confine the core within the sheath. Because the linear ignition fuze of the present invention requires only a single strand core having a closed curve cross section, as opposed to a bundle of three or more strands, a cruciform or other oddly shaped cross section that is difficult to manufacture in an extrusion process, the present invention provides a highly cost-effective, easily produced linear ignition fuze having performance equivalent to the more expensive prior art linear ignition fuzes.